Animate properties in GLSL shading
Hover the mouse over a field on the materials tab (alpha channel on this example)



and press i to insert a key. 
Move a few frames ahead (arrow keys), change the value and press i again to insert a new key.



We now have a spline animating that field from one value to the other. It works just like normal animation.



A grey button means there are no keyframes. A yellow color means There is a keyframe on that frame, a green button means that the values have been animated, but there is not a keyframe on that specific frame.

An alternative to pressing the letter i is to right click on the value you want to animatate and select Insert Keyframe;